Liquid crystal display devices, having low-profile, lightweight, low-power-consumption features, have been widely used in various fields such as banking terminals such as ATMs (automated teller machines), personal computers, remote controllers, and various monitors. Especially, in recent years, thanks to their features above, liquid crystal display devices have been especially suitably used for mobile applications such as electronic organizers, PDAs (personal digital assistants), and cellular phones.
In most cases of such applications, various operations are carried out by: placing a touch panel as a coordinate input device on a liquid crystal panel in a liquid crystal display device; and inputting coordinates pointed at by either pressing a surface of the touch panel with a finger directly touching the surface or pressing the surface with a touch pen or the like. A liquid crystal display device is also known whose liquid crystal panel has a coordinate input function instead of having a touch panel placed thereon.
In such liquid crystal display devices or, in particular, in a liquid crystal display device that is used for mobile applications, a vertical alignment liquid crystal panel referred to, for example, as the VA (vertical alignment) mode is suitably used because of its higher contrast than any other display modes. Among them, a vertical alignment liquid crystal panel referred to as the MVA (multi-domain vertical alignment) mode, in which the tilt direction of liquid crystal molecules in the presence of an electric field is divided into a plurality of directions by providing slits in pixel electrodes on an active matrix substrate and providing protrusions (ribs) as part of counter electrodes on a counter substrate, is especially suitably used because of its wide viewing angle.
However, such a liquid crystal display device suffers from pressure unevenness in display (white unevenness) when its touch panel is pressed with a touch pen or the like.
Application of pressure force to a surface of the touch panel with a touch pen or the like causes a slight change in cell thickness of the area subjected to the pressure force.
Conventionally, various improvements have been suggested to reduce cell thickness variation, for example, by placing a large number of columnar spacers.
For example, Patent Literature 1 discloses a technique by which in a bending-prone liquid crystal electro-optic device such as a 40-inch class of large-screen television, a pair of translucent substrates that form a liquid crystal cell are bonded together by curing a resin material to form resin spacers between the translucent substrates as means for preventing cell thickness variation from being caused when the liquid crystal panel is propped up.
According to Patent Literature 1, first, a mixture containing a liquid crystal material, a resin material, and an initiating reagent is heated until the liquid crystals exhibit an isotropic phase and sandwiched between a pair of translucent substrates kept at a constant interval by bead spacers. After that, by gradually lowering the temperature to separate out the resin material contained in the mixture, the liquid crystal material and the resin material were separated from each other. Next, by irradiating the mixture with ultraviolet rays to cleave the initiating agent and cure the resin material, resin spacers are formed between the translucent substrates.
Further, Patent Literature 2 discloses a technique for, in order to suppress the flowage of liquid crystals due to pressure, forming columnar spacers, having an average diameter of 2 to 50 μm, whose surfaces make contact with both the electrode substrate and the counter substrate.
According to Patent Literature 2, first, a coating liquid obtained by dissolving or dispersing a liquid crystal material, bead spacers, and a non-liquid-crystal polymer in or into a solvent is applied to the electrode substrate. Next, by producing an increase in temperature after evaporating the solvent and putting the counter substrate above the electrode substrate, islands of a cured product of the non-liquid-crystal polymer are grown and cured to be columns supporting both the substrates. Thus, columnar spacers are formed whose surfaces make contact with both the substrates.
Patent Literature 3 discloses a technique for, in order to suppress such problems that a low arrangement density of columnar spacers results in a lack of strength to cause unevenness of cell gap due to pressure and that the liquid crystal material is unevenly distributed by gravitation generated when the liquid crystal panel is propped up, controlling cell thickness by setting the spring constant of columnar spacers per unit area within a predetermined range.